I'm nearly positive this can be done, as I believe I have seen it before a few years ago (not here but somewhere on the web)

What I need is a circuit that would detect when headphones were plugged into a phono jack, then open a relay or transistor or w/e

Here's the project. I'm adding a FM transmitter to my car but it connects between the radio and antenna so the signal is near perfect. The problem is, there is a switch to turn it on and off. If it were to always be on, I wouldn't get radio.

I'm looking for a way to replace this switch with something that would detect that headphones have been plugged in and would then activate the power for me, but at the same time then kill the power once the headphones are removed.

thanks for the help guys, i'm really stumped on this one.

 

I do not see how RF into an antenna line and headphones plugged into a phono jack relate in a car,

Whatever magic you are doing, on which side of the signal should the detection be? At the plug side or the jack side?

Seen RCA jacks assemblies and also 1/4" jack assemblies with an attached microswitch pushed by the tip of the plug to signal insertion to other circuits. Seen both with cancelling extra contacts too. Not with plugs.

Miguel

 

the female end would be the one that does the detection.

If you don't see how all that goes together in a car, google "fm ipod transmitter" and then imagine that hard-wired into the car and into the antenna to get a better signal.

Thanks for the help


if you could put up a link to one of those phono jacks that has a switch bult in, that would be helpful as I don't really need to make a circuit, a switch would be best.

 

Hi.
Try securing a microswitch to the body of the FM modulator in such way that insertion of the plug displaces the actuating cam switching the power on.

I do not have that need in my car as I supplied permanent ACC +12V to the transmitter and installed a 3V regulator in its battery compartment, and plugs to a removable CD source.
Miguel

 

would this work?

http://www.allelectronics.com/make-a-store/item/SMJ/3.5MM-STEREO-PHONE-JACK-W/N.O.-SWITCH/1.html

I'm a little confused how a switch would work on it. I only see three connections which would be: right, left, and ground. Am I missing something?

 

That particular jack picture in the link may not correspond to the specified in the text; and it may have the switch sharing one pole with the audio path which does not make it useable for switching power.

A microswitch secured outside of the jack could be positioned in such way that the 'handle' part of the plug clicks it on by pure mechanical 'interference' positioning. I do not know of a better way to express it.
It may end bulky, ugly, but has to work. Seen lots of tiny mechanical microswitches inside printers and fax machines that the presence of paper actuates them. Well, make the body of the plug actuate it when inserted.

Take it as if I am changing the title of your original post as to "plug insertion detection" instead of the imprecise "headphone detection"

Miguel